Reverse-flow reactors are well known in the art. The general principle of such reactors has been described in detail in “Reverse-Flow Operation in Fixed Bed Catalytic Reactors”, Cata. Rev.-Sci. Eng., 28(1), 1-68 (1996).
Reverse-flow reactors have been employed in a number of different large-scale heterogeneous processes, such as catalytic incineration of volatile organic contaminants, the hydrogen sulphide oxidation by sulphur dioxide, Fischer-Tropsch synthesis over ruthenium and cobalt catalysts, the selective reduction of carbon monoxide and/or nitric oxides in flue gases, and similar processes, as described in U.S. Pat. No. 6,261,093, CAN-A-1,165,264, U.S. Pat. No. 5,753,197, U.S. Pat. No. 5,589,142.
A simple reverse-flow reactor for catalytic reactions on a fixed catalyst bed consists of a reactor vessel comprising at least one catalyst bed and optionally, one or more beds of refractory packings, often referred to as inerts to hold the catalyst bed in place which also may provide for additional heat capacity, and the necessary line-up and switching valves that allow to oscillate the flow direction of a fluid or gaseous reaction medium between the respective reactor in- or outlet.
A disadvantage of all fixed bed reactors, and hence also of reverse-flow reactors is that contaminants present in the reaction medium may deactivate or reduce the selectivity of the catalyst, and thus require replacement or reactivation of the catalyst. Due to the complex structure of a reverse-flow reactor set-up, such reactivation or replacement is particularly cumbersome. Alternatively, the contaminants need to be removed from the reactor feeds before feeding into the reverse-flow reactor, which requires an additional separate removal step involving costs for operation and investment.
The subject invention has the advantage to avoid the deactivation of the catalysts without the requirement for a separate removal step.
This has been achieved by placing at least one bed of a selectively adsorbing material before each side of the catalyst bed.